Voltage responsive screen control methods and systems



June 1959 H. P. KALLMANN ET AL 2,392,968

VOLTAGE RESPONSIVE SCREEN CONTROL METHODS AND SYSTEMS Filed Oct. 25,1956 2 Sheets-Sheet 2 FIG. 2.

MODU- LA TOR F01? WA RD V01. 77165 500,965

Pill. 55 .7/

AMPL lF/El? 5 WE E F CONT REVERSE BLANK IN6 VOL 7' A65 BAH/g7 ROSENBERG@463; NW Till/M ATTORNEY5 United VOLTAGE RESPONSIVE SCREEN CONTROLMETHODS AND SYSTEMS Hartmut P. Kallmann, Riverdale, and BarnettRosenberg, New York, N.Y., assignors to Research Corporation, New York,N.Y., a corporation of New York Application October 23, 1956, Serial No.617,739

7 Claims. (Cl. 315-169) This invention relates to voltage-responsivescreen control methods and systems for energizing selected localizedregions in a screen containing voltage-responsive material, whileavoiding undesired energization of other regions in the screen. Themethods and systems of the present invention are highly suitable for usein the electrical recording, storage and recalling of information and indisplaying information such as wave forms, patterns, coordinate values,and other data, and are particularly well adapted and advantageous forfiat-screen television. The methods and apparatus of the presentinvention are very well adapted for use with screens utilizingvoltage-responsive material and wherein during operation variouslocalized regions of the screen are selected and energized by theapplication of voltage difierentials thereto. In the control methods andapparatus of the present invention selected localized regions orelemental volumes of voltageresponsive material are energized byvoltages applied in the forward direction through unidirectional currentconducting means.

Among the many advantages of the illustrative embodiments of the presentinvention described herein are those resulting from the fact that otherelemental volumes of the voltage-responsive material are maintained in asubstantially unenergized condition. That is, they remain blankedout.They are blanked out by voltage diiierentials acting in the reversedirection through the unidirectional current conduction means.

The methods and apparatus of the present invention are highly adaptedfor use with screens including pairs of control grids for energizingselected localized regions or elemental volumes of the screens and areparticularly advantageous for display screens such as fiat televisionscreens including material emitting visible light at selected energizedareas as controlled by the control grids.

A number of important advantages result from the methods and apparatusof the present invention when applied to electroluminescent displayscreens for showing television pictures. The illustrative embodiments ofthe present invention utilize electroluminescent materials in flattelevision screens. The brilliance and distinctness of the illuminatedspots in the display screen are greatly enhanced by the presentinvention.

In the illustrative method described as embodying the present invention,the excitation voltage is applied in the forward direction throughunidirectional current conduction means to selected pairs of conductiveelements of the two control grids and thus to the desired selected ele--mental volumes of the electroluminescent material at juncture points soas to create visible light at these desired points. In the methoddescribed any undesired excitation of the electroluminescent material isprevented by the application of blanking voltages. These blankingvoltages are applied in the reverse direction through unidirectionalcurrent conduction means to other respective conductive elements of thetwo grids, thus controlling the electric fields within the elementalvolumes of the electroluminescent material at other respective juncturesin the 2,892,968 Patented June 30, 1959 ice screen and suppressing anycreation of visible light at these other points.

Electroluminescent materials have the property that the application ofan electric field through an elemental volume of the material causesthat volume to emit visible light. Electroluminescent materialsgenerally exhibit the characteristic that the light output over a rangeof values rises very rapidly with the magnitude of the applied voltage.

In electroluminescent display screens a pair of grids of conductiveelements are arranged in spaced relationship so that the variousconductive elements of the two grids pass near to each other at numerousspaced juncture points. Electroluminescent material is positionedbetween these grids at these junctures. When voltage differentials ofthe proper values are applied between selected conductive elements inthe two grids, light is emitted from the volumes of theelectroluminescent material located at the points where the energizedconductors pass near each other. The electric fields created within thebody of the electroluminescent material in the screen by the appliedvoltages are strongest at the points where these conductors pass mostclosely together. Thus, the emitted light is brightest at these points.But, in display screens as known prior to our invention, the appliedvoltages also created undesired strong fields at other regions withinthe body of the electroluminescent material in the screen.

One of the problems which has seriously interfered with the operation ofprior electroluminescent screens is the fact that such undesiredsubstantial voltage fields are created along the full lengths of theenergized conductive elements in the grids. This causes undesiredvisible light to be emitted along the lengths of these conductiveelements. This background of light is confused with the brighter pointof light created at the juncture points of the energized elements. Inoperating prior electroluminescent display screens wherein the two gridsare arranged at right angles to each other, the effect is to createcrosses of light with brighter spots appearing at the juncture point.Thus, there is a lack of distinctness and clarity in the informationdisplayed in prior screens. The brilliance and contrast which can beobtained from prior screens is very limited.

Moreover, in prior screens there is the added difi'iculty that thebrightness which can be obtained for the viewer is drastically limited.This brightness is limited by the undesired creation of backgroundillumination. Any attempt to increase the brightness at the desiredpoints by increasing the applied voltage in prior screens also causes alarge increase in the background illumination. The effective increase inbackground illumination as seen by the viewer, more than offsets theincrease in brightness at the desired points.

Elforts have been made in the past without much success in trying toovercome this problem. These have involved the use of specializedelectroluminescent materials and have attempted to utilize specializedphase relationships within the electroluminescent material in an effortto increase the desired brightness While suppressing the undesiredexcitation in neighboring areas.

Among the advantages of the present invention are those resulting fromthe fact that an increased voltage field is applied at the desired pointor points within the various elemental volumes of the electroluminescentmaterial while greatly minimizing any undesired fields at other pointswithin the display screen. In this way the brilliance of the light fromthe desired points is greatly increased while at-the same time theundesired background light caused by undesired excitation of theelectroluminescent material is markedly decreased.

Among the many further advantages of the present invention are thoseresulting from the fact that it improves the definition, clarity, andbrightness characteristics of the display screen thus greatly enhancingthe usefulness and intelligibility of the displayed information. Theresult is a big improvement in fiat-screen television display systems.

It is among the objects of this invention to provide anelectroluminescent display screen control method and apparatus havingimproved definition and brightness characteristics.

Among the further important advantages of the present invention arethose resulting from the fact that it enables an increased operatingvoltage differential to be applied at any desired point within theelectroluminescentmaterial while decreasing the effective voltagediiferential applied to the other areas where no light output isdesired. The resulting improvement in definition arid brilliance in manycases is of the order of hundreds of times that in prior screens. Thepresent invention enables the rising light output characteristics ofelectroluminescent materials with respect to applied voltage to beutilized to great advantage. By virtue of the markedly increased voltagedifferentials obtainable in operation the light output from the desiredpoints is increased by substan tial amounts, which in many cases are ofthe order of hundreds of times that avialable in the prior art, whilethe background illumination is actually decreased markedly below thatobtainable in any prior art screens of which we are aware.

In this specification and in the accompanying draw ings are describedand shown, electroluminescent display screen control methods and systemsembodying our invention and various modifications thereof are suggested,but it is to be understood that these are not intended to be exhaustivenor limiting of the invention, but on the contrary are given forpurposes of illustration in order that others skilled in the art mayfully understand the invention and the manner of applying the method andapparatus in practical use so that they may modify and adapt it invarious forms, each as may be best suited to the conditions of aparticular use.

The various aspects, objects and advantages of the present inventionwill be more fully understood from a consideration of the followingspecification in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic circuit diagram with portions being shown inperspective and cut-away, illustrating a voltage-responsive screencontrol method and apparatus embodying the present invention; in thisillustrative embodiment the screen is shown as being anelectroluminescent display screen;

Figure 2 is a schematic circuit diagram of a modified method andapparatus similar with that illustrated in Figure 1;

Figure 3 is a schematic circuit diagram of a portion of the displayscreen of Figure 1 and of Figure 2 for purposes of explaining theimproved operation;

Figures 4A and 4B are schematic circuit diagrams for purposes ofexplanation;

Figure 5 is a graphical type representation of the way in which thelight output from electroluminescent materials generally rises muchfaster than the applied voltage over a range of values;

Figure 6 is an illustration used in connection with an explanation ofthe prior art and its limitations.

As shown in Figure 1, the electroluminescent display screen, generallyindicated at 10, includes a suitable rigid planar support member orbacking 12 of inert electrically insulating material. For example, thissupport may be a plate of glass, or a plate of Lucite or Plexiglas(methylmethacrylate). A grid of inert condu'ctiveele ments or strips 14extends across the front face of the support 12 and ar'eshown in spacedparallel relationship insulated from each other. When a glass backing.12 is used, these conductive elements 14 are strips of conductive glassmaterial, such as tin oxide glass, extending across the face of thebacking. Also, it is satisfactory to use chemically deposited orevaporated metal conductors 14, of materials such as copper, aluminum,gold, and silver, suitably spaced as by etching or by scribing.

For purposes of clarity in illustration, these conductive elements 14are shown as being spaced a considerable distance apart. But in thetypical screen 10, these conductors are often quite closely spaced, forexample, as many as 50 or conductors per lineal inch may be used,depending upon the total area of the screen and upon the distance fromwhich it is to be used. For cinema type electroluminescent displayscreens the total area is much greater and only a few conductiveelements 14 per inch are used.

Overlying the grid of conductors 14 is a layer or slab ofelectroluminescent material 16. A layer of zinc sulfide copper-activatedmaterial has proven very satisfactory. Other electroluminescentmaterials such as zinc selenide or cadmium sulfide activated with coppermay also be used.

This electroluminescent layer may satisfactorily be prepared bydispersing the powdered electroluminescent phosphor material in meltedcastor wax. This melted electroluminescent matrix is then spread in alayer having a thickness in the range from one to ten mils over theconductors 14-. We have found that an electroluminescent layer 5 milsthick is preferable for most applications as giving good definition plusbrilliance. Next, a transparent covering plate 18 is placed over thematrix layer 16. This transparent covering plate has a grid ofconductive elements 20 extending across its lower face in spacedparallel relationship insulated from each other. This cover plate ispressed down upon the molten matrix of castor wax and phosphor materialso as to exclude the air, and the castor wax is allowed to harden.

The conductors 20 are transparent. They may satisfactorily be preparedby evaporating thin plating of conductive metal such as gold, silver,copper, or aluminum upon the undersurface of the cover plate 18. When aglass covering plate is used, they may satisfactorily be formed bystrips of conductive tin oxide glass. The conductive plating ma beetched or scribed to produce the individual conductive elements 20insulated from each other.

In the foregoing description we have set forth certain desirablematerials which may be used to advantage in constructing theelectroluminescent display screen 10. However, it is to be understoodthat it is an advantage of the present invention that anyvoltage-responsive ma terial may be used which has the characteristicthat one of its characteristics at least over a suitable operating rangechanges with increased voltage differential applied thereto. In theillustrative display screen shown any electroluminescent material may beused which has the characteristic that its light output at least over asuitable operating range increases with increased voltage differentialapplied thereto. Any inert insulating material having good insulationstrength may be used to provide the backing 12. Similarly, any suitablematerial rn'ay be used to provide the transparent cover 18 and thetransparent conductors 20.

Regardless of the particular materials which are used, it is importantthat the screen 10 be constructed such that the total resistance asmeasured along the length of each of the conductive elements 14 andalong the? length of each of the conductive elements 20 should bemarkedly less than the total resistance at each juncture point from aconductor 14 to a conductor 20 through the electroluminescentmaterialle. For example, we find that it is desirable to have theresistance measured through the layer 16 ateach juncture at least 100times as large as the resistance measured along the lengths of theindividual conductors 1'4 and 2t),

In order to control the electroluminescent screen, each of theconductive elements is connected by a lead 22 to unidirectional currentconduction means 24, shown as pairs of rectifiers in series. Theserectifiers all have the same conductive relationship with the respectiveconductive elements to which they are coupled. They are shown as havingtheir favored (i.e. low resistance) direction of conduction facingforward toward these conductive elements. These conductive elements arecontrolled by conductive means including a first source of controlvoltage 26, called the forward voltage source and including a secondsource of control voltage 28 called the reverse blanking voltage source.

In the control system shown, the forward voltage source supplies directvoltage at three terminals 30, 31, and 32. The center terminal 31 isneutral and is connected to the common return circuit of the system, asin-, dicated by the ground connection symbol. The positive terminal isconnected by a lead 34 to selective energizing means, generallyindicated at 36, and including a first wiper switch 38 and a secondwiper switch 40 which are ganged together and driven in synchronism by asynchronous type motor 42.

In order to feed voltage in the forward direction selectively throughthe unidirectional current conduction means 24, the lead 34 is connectedby means of a slipring and wiper arm 44 of the switch 38 to the variousswitch contacts 46. From each of these contacts 46 the control circuitpasses by way of individual leads 48 through the respective rectifiers24 to the conductive elements 20.

In this control system the negative terminal 32 of the forward voltagesource is connected by a lead 50 through a modulator 52 and by a lead 54to second selective energizing means, generally indicated at 56. Thissecond selective energizing means includes a first wiper switch 58 and asecond wiper switch 60, which are ganged together and driven insynchronism by a synchronous type motor 62.

In this control system the first and second selective energizing means36 and 56, respectively, are identical in construction, except that thedriving motor 62 is energized to rotate the switches 58 and at a slowerrate than the corresponding switches 38 and 40. This difference inswitching speeds produces the desired different horizontal and verticalrates of sweep of the illuminated spot across the screen 10, inaccordance with the type of information being displayed. For atelevision type of display, the picture is produced by rapidly sweepingthe illuminated spot horizontally to paint the horizontal line segmentsof the picture and by progressing vertically at a correspondingly slowerrate from one line segment to the next. For such a display, the switches38 and 40 are driven at a rapid rate to create the line segments of thepicture in the screen 10 while the switches 58 and 60 movecorrespondingly slower.

The various conductive elements 14 in the other control grid areindividually connected by leads 64 to second unidirectional currentconduction means 66 shown as pairs of series connected rectifiers. Theserectifiers are all arranged in the same conductive relationship withrespect to the associated conductive elements 14. Their favoreddirection of conduction, that is, the direction of low resistance, isfacing away from the conductive elements 14. These pairs of rectifiers66 are connected by leads 68 to the respective contacts 70 of the wiperswitch 58. The return circuit from the contact 70- is completed througha rotating wiper contact and slip-ring 72 to the lead 54. r

In operation, as the contact arms 44 and 72 rotate, they selectivelyapply a voltage field across elemental volumes of the electroluminescentmaterial at the various juncture points in the screen 10, causing thesevarious points to emit visible light. The forward control circuit forenergizing the desired points can be traced from the positive terminal30 through the lead 34, the slip-ring and arm .44, any one of thecontacts 46, a corresponding lead 48 and through the corresponding pairof rectifiers 24 and by a lead 22 to the corresponding one of theconductors 28. The return circuit passes from any one of the conductiveelements 14 through the corresponding lead 64 and a corresponding pairof rectifiers 66 and a lead 68 to one of the contacts 70 and thencethrough the arm and slip-ring 72 to the lead 54 and back through themodulator 52 and through the lead 50 to the negative terminal 32.

For interlaced scanning as now used in commercial television, alternateones of the leads 68 are connected in succession to adjacent contacts 70over one-half of the switch 58, and the respective intermediate leads 68are connected in succession to adjacent contacts 70 over the otherone-half of the switch 78.

The modulator 52 controls the strength of the voltage field appliedthrough the electroluminescent material at the respective juncturepoints of the screen 10 and thus controls the relative intensity of thelight emitted-at the various points of the screen 10 in accordance withthe information being displayed. The modulator 52 may be any electricalvalve whose effective conductivity is controllable in response to acontrol signal fed in through the control line 74. For example, a triodemay be used with the anode circuit connected to the lead 54, and thecathode circuit connected to the lead 50; the grid is controlled by line74.

In prior art electroluminescent screens, as schematically indicated inFigure 6, the operation of the screen produces a band of illumination atall points along the length of the grid conductor 20a which isenergized. This background illumination results from the electric fieldwhich is created along the length of the conductor 20a. For example,assume that a positive voltage of say 50 volts is applied to theconductor 20a. That is, the voltage being applied to the conductor 20ais assumed to be 50 volts more positive than that of theelectroluminescent layer. At all points along the length of thisconductor 20a a voltage difference of 50 volts now exists between theconductor 20a and the body of the electroluminescent material, and thisvoltage difference causes the electroluminescent material to emit theband of light 80.

Similarly, assume that a negative voltage of 50 volts is applied to thegrid conductor 14a. A band 82 of background illumination is created atall points along the length of the conductor 14a as a result of thevoltage differential between the conductor 14a and the body of theelectroluminescent material. At the juncture point where the conductiveelements 14a and 20a approach each other most closely, a total voltagedifference of volts is applied across an elemental volume of theelectroluminescent material causing a brighter spot as indicated at 84.

Efforts have been made prior to the present invention to overcome thisproblem by operating the conductors of one of the grids at the samevoltage as the body of the electroluminescent material, by grounding.This does not solve the problem because the conductors of the other gridmust then be operated at twice the voltage differential with respect tothe body of the electroluminescent material to obtain the samebrilliance at the spot 84. As a result, a much brighter band ofbackground illumination is created along the energized conductor.

In order to prevent any background illumination, a blanking voltage isapplied in the reverse direction through the unidirectional currentconduction means 24 and 66 to all of the conductors 14 and 20 which arenot being used to energize the desired spot in the screen 10.

Consideration is now directed to Figures 3, 4A and 4B in conjunctionwith Figure 1. For purposes of explanation, assume that a positivevoltage as indicated by (Figure 3) of, say, 50 volts is applied in theforward direction through a pair of the rectifiers 24' to energizeaselected one'of the conductors 2 A return circuit is completed from aselected conductor 14' in the other grid by appl-ying a negative voltageas indicated by (Figure 3) of, say, 50 volts through a pair of therectifiers 66 in the forward direction. As a result, an elemental volumeof electroluminescent material 86 at their juncture point is brightlyilluminated, as desired.

This energizing voltage is applied in the forward'directron through therectifiers 24' and 66 so that, as indicated in Figure 4B, they offer arelatively small resistance 'to the applied voltage. These rectifiers.24' and '66 are effectively in series with the elemental volume '86, andbecause of their low forward resistance, only asm'all voltage drop sappears across them. Most of the applied voltage appears acrossthe'elemental volume 86 as indicated at V creating an intense electricfield and brilliantly lighting this spot 86.

At the same time, positive blanking voltages of, say, 50 volts areapplied in the reverse direction through the other pairs of rectifiers66 to the other conductors 14 whilea return circuit is completed in thereversedirection through the other rectifiers 24 by applying negativevoltages of, say, 50 volts, as indicated in Figure 3.

Advantageously, all of the other elemental volumes 88 ofelectroluminescent material along the positively ener- I the negativelyenergized conductive element 14' are now at juncture points with theother conductive elements 20 which are also being subjected to negativevoltages applied in the reverse direction through the rectifiers 66.Thus, these elemental volumes are desirably held blanked out regardlessof the magnitudes of the forward voltages on-the elements 14 and 20'.

With regard to the other elemental vohunes 92 at other points (i.e. notalong the forwardly energized conductive elements 14 and 20'), it isseen that the blanking voltages are applied effectively in a seriescircuit through the rectifiers 24 and 66 in the reverse high resistancedirection. Thus, as indicated in Figure 4A, the great major portions mof the reverse blanking voltage appears across the rectifiers 24 and 66.Only a very tiny fraction V of this voltage appears across each of thevolumes 92. Thus, the volumes 92 are also maintained substantiallycompletely blanked out while the volume 86 is brilliantly illuminated.

As a result of this advantageous operation, the forward voltages can beincreased to much larger values than possible heretofore with comparableelectroluminescent materials. The result is a many-fold increase inbrilliance, definition and clarity. As diagrammatically illustrated inFigure the light output from electroluminescent materials over a rangeof values generally increases rapidly and at an increasing rate withapplied voltage. Thus, the increases in applied voltage obtainable withthe present invention often provide an increase in light output of 100times or more for the same background illumination.

The baclrresistance, or reverse resistance of the unidirectional currentconduction means 24 and 66 is preferably substantially greater than theresistance through the layer of electroluminescent material. Withelectroluminescent materials of the type giving a resistance through thelayer 16 of a relatively low value, say less than a million ohms, thengermanium type rectifiers may be used arranged to provide a reverseresistance of at least two million ohms or more.

With higher resistance layers 16, vacuum tube recti- 8 fiers maybe used.We have foundthat even with phosphor materials having a specificresistivity as high as 10 ohm-centimeters, highly satisfactory resultsare obtained by using tube rectifiers such as 6H6s.

To apply the reverse blanking voltage, the negative terminal 94 -of thesource 28 -is connected through a lead 98 to -a conductive commutatordisk 100 of the switch 40. This disk 1'00 has an insulating notch in itsperimeter and thus engages all of the contacts 102 except the contactcorresponding in position with the contact 46 being energized by thewiper arm 44. Corresponding contacts 46 and 102 of the switches 38 and40 are connected together by jumper leads 104 as shown.

The neutral terminal 95 of the source 28 is grounded, and the positiveterminal 96 is connected through a lead 106 to a commutator disk 108 ofthe switch 60 engaging all of the contacts 110 except that correspondingwith the position of the arm 72 in the companion switch 58. Jumper leads112 connect corresponding contacts 70 and 110.

In order to modulate the brilliance of the various bright spots so as todisplay the desired intelligence, for example to display a televisionprogram, an antenna 114 picks up the desired signal. This is amplifiedby the video amplifier and sweep control 116, the amplified signal beingapplied to the control line 74.

As indicated schematically by the lines 118 and 120, the control 116provides signals for synchronizing the sweeping speeds of the motors 42and 62.

The control system of Figure 2 is generally similar to that of Figure 1and corresponding reference numerals are used in these two figures forparts performing corresponding functions.

The selective energizing means 36 for applying energizing voltage toselected conductive elements 20 includes a pulse generator 121 coupledthrough an isolating capacitor 122 to a lead 124 connected to anelectrical delay-line network 126. This delay line includes a pluralityof identical inductors 128 connected in series with a plurality ofcapacitors 130 connected in shunt across the line at the junctions ofthe respective inductors. The terminals of this delay line are indicatedat 129 and 131.

A terminating impedance 132 having a value of Z corresponding with thecharacteristic impedance of the line is connected across theend-opposite to the input end which is fed by the lead 124. A positivevoltage is fed via the lead 34 into the pulse generator, which suppliessharp square-wave pulses of positive voltage to the delay line. As thesepositive voltage pulses travel down the delay line from the inputterminals 129 and 131 toward the terminating impedance 132, successiveleads 48 have brief positive voltage pulses applied thereto to producethe desired sweep. The termination 132 prevents reflections back downthe line. The other input terminal 131 is connected to the other outputterminal of the pulse generator by a lead 133 which is. grounded.

The pulse generator 121 may be a multivibrator circuit or a Schmidttrigger circuit controlled by the video amplifier and control 116 asdiagrammatically indicated by the connection 134.

In order to blank out the other spots in the screen 10, a negativereverse blanking voltage is applied from a negative terminal 94 of thesource 28 through the lead 98 and an isolating resistor 136 and througha lead 138 to the lead 124 feeding into the delay-line terminal 129.This negative voltage holds all the inductors 128 negative except at theplace along the delay-line being traversed by the positive voltage pulsefrom the generator 121.

For purposes of emphasizing the desirability of utilizing unidirectionalcurrent conduction means having a high resistance in the reversedirection, pairs of seriesconnected rectifiers are shown in Figures 1,2, and 3. When the back resistance of the rectifiers being used is lowerthan the desired relationship to the resistance ofthe electroluminescentlayer 16 than that expressed above, then two or more rectifiers maydesirably be connected in series as shown. Where each rectifier has arelatively high back resistance, then a single rectifier may be used.

As will be understood from the above specification the unidirectionalcurrent conduction means 24 and 66 are intended to operate to minimizeresistance in the energizing circuit while maximizing the resistance inthe blanking circuits. The concept of our invention includes means otherthan rectifiers for providing low forward resistance and high backresistance. The claimed method includes the steps of applying anenergizing voltage in the forward direction through a low resistancepath to selected elemental volumes of the" electroluminescent material,and simultaneously applying a blanking voltage of opposite polaritythrough high resistance paths to elemental volumes other than saidselected ones.

The return circuit for the forward energizing voltage is traced throughthe switch 58 corresponding to that in the system of Figure 1.

The reverse blanking circuit is completed to the positive terminal 96through the lead 106 from the switch 56 as in the system of Figure 1.

From the foregoing it will be understood that the electroluminescentdisplay screen control methods and systems of the present inventiondescribed above are well suited to provide the advantages set forth, andsince many possible embodiments may be made of the various features ofthis invention and as the method and apparatus herein described may bevaried in various parts, all without departing from the scope of theinvention, it is to be understood that all matter hereinbefore set forthor shown in the accompanying drawings is to be interpreted asillustrative and not in a limiting sense and that in certain instances,some of the features of the invention may be used without acorresponding use of other features, all without departing from thescope of the invention.

We claim:

1. An electroluminescent display screen control system comprising afirst grid of spaced parallel conductors, a second grid of spacedparallel conductors in spaced electrically insulated relationship withsaid first grid, the conductors of said second grid being axiallyaligned at a substantial angle with respect to the axes of theconductors of said second grid, a layer of electroluminescent materialpositioned between said grids, first unidirectional current conductionmeans readily conducting current in a favored direction and resistingflow of current in the reverse direction and being connected to therespective conductors of said first grid in relationship to favor theconduction of current to said conductors, second unidirectional currentconduction means readily conducting current in a favored direction andresisting the flow of current in the reverse direction and beingconnected to the respective conductors of said second grid inrelationship to favor the conduction of current away therefrom, acontrol voltage source, circuit means selectively applying said controlvoltage through said first unidirectional current conduction means inthe favored direction to a respective one of the conductors of saidfirst grid and selectively returning said control voltage through saidsecond unidirectional current conduction means in the favored directionfrom a respective one of the conductors of said second grid, andincluding means selectively applying a blanking voltage in the reversedirection through said first unidirectional current conduction means toother respective conductors of said first grid and selectively returningsaid blanking voltage in the reversed direction through the secondunidirectional current conduction means from other respective conductorsof said second grid.

2. In the art of operating electroluminescent display screens of thetype including first and second grids of conductive elements arrangedselectively to energize elemental volumes of electroluminescentmaterial, the improved method for increasing the brilliance whilepreventing undesired background illumination comprising the steps ofapplying a blanking voltage in the reverse direction throughunidirectional current conduction means to all of the conductiveelements of said first grid except at least one while providing a returncircuit for said blanking voltage through all of the conductive elementsof the second grid except at least one, and simultaneously applying avoltage in the forward direction through unidirectional currentconduction means to one of the other conductive elements of the firstgrid and providing a return circuit for said voltage through one of theother conductive elements of the second grid.

3. An improved electroluminescent display screen control systemproviding increased brilliance at the desired juncture points whileblanking out the remainder of said screen and comprising a first grid ofconductive elements in insulated relationship, a second grid ofconductive elements in insulated relationship and spaced from said firstconductive elements forming spaced junctures therewith,electroluminescent material between said grids, unidirectional currentconduction means connected to the respective conductive elements of oneof said grids and all having the same direction of conduction, firstselective energizing means arranged to complete an energizing circuitthrough the unidirectional current conduction means and through selectedconductive elements of said one grid and through said electroluminescentmaterial and through selected conductive elements of the other grid,said energizing circuit including energizing voltage applied in theforward direction through the unidirectional current conduction means,thereby to energize the electroluminescent material at the junctures ofthe selected conductive elements of said grids, second selectiveblanking means arranged to complete a blanking circuit through theunidirectional current conduction means and through other selectedconductive elements of said one grid and through said electroluminescentmaterial and through other selected conductive elements of the othergrid, said blanking circuit including blanking voltage applied in thereverse direction through the unidirectional current conduction means inthe reverse direction, thereby to prevent any substantial illuminationof the electroluminescent material at other junctures.

4. An electroluminescent display screen control system including a layerof electroluminescent material which admits light when an electric fieldis applied thereacross, a first grid including a plurality ofnon-intersecting conductors arranged along one surface of saidelectroluminescent layer, a second grid including a plurality ofnon-intersecting conductors arranged along the opposite surface of saidelectroluminescent layer, said grids being so oriented that projectionsof both grid structures form an intersecting pattern, a plurality ofunidirectional current conduction elements connected to the respectiveconductors of said first grid in a first conductive relationship withrespect thereto, a second plurality of unidirectional current conductingelements connected to the conductors of said second grid in a reversecurrent conducting relationship therewith, first switching meansarranged to apply voltage in a forward direction through one of saidunidirectional current conducting elements of the first plurality to oneof the conductors of said first grid and arranged to complete a circuitthrough one of said unidirectional current conducting elements of thesecond plurality to one of the conductors of said second grid, andsecond switching means arranged to apply voltage in a reverse directionthrough said unidirectional current conducting elements of the firstplurality to the other conductors of said first grid and completing acircuit through the unidirectional current conducting elements of thesecond plurality to the other conductors of said second grid.

5. A flat screen television control system comprising 11' first andsecond grid structures of spaced parallel conductive elements in spacedinsulated relationship with oneanother so positioned that projections ofboth grid structures form an intersecting pattern, voltage-responsivelight-emitting material at the points where thecon-r ductive elements ofthe first grid structure approach closest to the conductive elements ofthe second gridv structure, a plurality of rectifier means all connectedin the same relationship to the conductive elements of the first grid,first switching means arranged to apply a control voltage in circuitfrom a selected one of the conductive elements of the first gridstructure through an elemental volume of said light-emitting material toa selected conductive element of said second grid structure and in theforward direction through one of said rectifier means, and secondswitching means arranged to apply a blanking voltage in circuit throughthe other conductive elements of the first grid structure and throughthe other elemental volumes and the other conductive elements of thesecond grid and through said rectifiers in the reverse direction, anelectrical delay line having spaced points therealong coupled to theconductive elements of one of said grid structures, a pulse generatorcoupled to one end of said delay line, an intensity modulator connectedto said first switching means, and sweep control means connected, tosaid first and second switching means for operating themin synchronism.

6. An improved electroluminescent delay screen control system providingincreased brilliance at the desired points while selectively blankingout other areas of the screen comprising a first grid of conductiveelements in insulated relationship with one another, a second grid ofconductive elements in insulated relationship with one another andspaced from the elements of the first grid and at an angle therewithforming spaced junctures between the respective elements of the grids, aplurality of unidirectional current conduction means connected to the respective elements of one of said grids and all having the same relativefavored direction of conduction with respect to the elements of said onegrid, first and second synchronized switch means, a plurality of,conductive means connecting said first and second switch means to theelements of the first grid, a forward voltage source connected incircuit with said first switch means and the elements of the secondgrid, a reverse blanking voltage source of opposite polarity from saidforward source connected in circuit with said second switch means andthe elements of the second grid, said first switch means selectivelyapplying said forward voltage source to at least one of the conductivemeans, said second switch means selectively applying said reverseblanking voltage source to other conductive means, a modulator forcontrolling the intensity of said forward voltage source, and controlmeans for operating said synchronized switch means.

7. An improved electroluminescent display screen as claimed in claim 6and including third and fourth switch means, a plurality of conductivemeans connecting said third and fourth switch means to the elements ofthe second grid, said third switch means being in circuit with saidforward voltage source, and said fourth switch means being in circuitwith said reverse blanking voltage source, said third switch meansselectively applying said forward voltage source to at least one of thesecond plurality of conductive means, and said fourth switch meansselectively applying said reverse blanking voltage source to others ofthe conductive means of the second plurality.

References Cited in the file of this patent UNITED STATES PATENTS2,313,286 Okolicsanyi Mar. 9, 1943 2,698,915 Piper Jan. 4, 19552,749,480 Ruderfer June 5, 1956 2,774,813 Livingston Dec. 18, 19562,818,531 Peek Dec. 31, 1957

